Dual lumen catheters are commonly used for transporting bodily fluids for treatment external of a patient's body, a process generally referred to in the medical field as “extracorporeal” treatment, and thereafter returning the treated fluid to the body. The fluid is withdrawn from the body through one of the lumens of the catheter, generally referred to as the withdrawal, or aspiration, lumen. The fluid is subjected to a treatment process, and thereafter returned to the body through the other lumen, generally referred to as the infusion, or return, lumen.
In many cases, the extracorporeal treatment is carried out as part of a hemodialysis procedure. During hemodialysis, blood is withdrawn from a blood vessel through the aspiration lumen and routed to a dialyzer for cleansing. The cleansed blood is then returned to the vessel through the infusion lumen. When such a catheter is used for hemodialysis, whether for acute (short-term, generally thirty days or less) or longer term hemodialysis, it is generally inserted into the body through the internal jugular vein, subclavian vein or femoral vein. In addition to hemodialysis, extracorporeal catheters can also be used for other procedures, such as pheresis and hemofiltration, in which a fluid is removed from the body for treatment and later returned to the body.
A variety of hemodialysis catheters are commercially available. Among the types of commercially available catheters are: 1) a dual lumen catheter having one lumen (e.g., the blood infusion lumen), that terminates distal to the other lumen (e.g., the blood aspiration lumen). Some catheters of this type are provided with a midline split between the withdrawal and infusion lumens, while others do not have such a split (e.g., the COOK® DDS catheter); 2) a catheter having a slitted valve in the distal tip that acts as a pressure valve opening. This valve opens inwardly for blood aspiration, outwardly for blood infusion, and remains closed when not in use (e.g., the Groshong catheter); 3) a cuffed central venous silicone catheter that is tunneled underneath the skin to reduce infection (e.g., Broviac, Leonard and Hickman catheters); 4) a dual lumen catheter having a tapered tip and two adjacent holes communicating with one lumen just proximal to the tip to assist with outflow, and two adjacent holes communicating with the other lumen (180 degrees removed) just proximal to the first set of holes to assist with inflow (e.g., the Mahurkar catheter); and 5) a dual lumen catheter having a diverting structure consisting of a shoulder that has a straight up distal face and a sloped proximal face to reduce access recirculation and raise pressure in the vicinity of the inlet aperture (U.S. Pat. No. 6,409,700).
One problem with existing multi-lumen catheters is that such catheters can experience decreased flow rates over time. Decreased flow rates may be caused by, among other things, blockage of the aspiration and/or infusion ports in the catheter. Various factors can cause a port to become blocked. One common cause of port blockage is the inadvertent positioning of one or more ports of the catheter against the vessel wall. This positioning hinders the free flow of fluid through the obstructed port, and in some cases, prevents fluid flow altogether. Another common cause of port blockage is the formation of fibrin sheaths along the ports. Fibrin sheaths may be formed, e.g., in response to the vessel wall washing effect or clotting.
Decreased, or restricted, flow is clearly undesirable in a multi-lumen catheter for use in extracorporeal treatment of a fluid, such as a hemodialysis catheter. In order for the extracorporeal fluid treatment to be effective, fluid flow through the catheter must not be restricted in any appreciable way. Thus, it is important to position existing catheters in a manner such that fluid flow is not restricted. Additionally, it is important to insure that all ports are unobstructed.
As indicated above, various attempts have been made in the art to reduce port blockage. Some catheters are provided with side ports at various locations on the catheter, which generally provide some reduction in port blockage, however such ports themselves are subject to blockage when placed against the vessel wall, or as a result of fibrin formation on the port. Other attempts have been made to reduce port blockage by providing the staggered side-by-side dual lumen design described above. Here, the respective aspiration and infusion tubes can be different lengths so that the ports aspirate and infuse the bodily fluid at different axial locations of the catheter, which can also reduce recirculation. While these, and other, arrangements may avoid some problems involved in maintaining adequate flow through the lumens, such catheters can still be subject to suboptimal flow. Some catheters, such as the Mahurkar catheter described above, must be rotated or repositioned if inflow is blocked because the catheter is up against the vein wall. Although each of these techniques may be at least partially effective in reducing some types of blockage, reduced flow rate continues to be a problem in the art.
It is desired to provide a multi-lumen catheter assembly for use in the extracorporeal treatment of bodily fluids, wherein the multi-lumen catheter assembly is structured in a manner to minimize port blockage, and to provide for optimal fluid flow through the lumens of the catheter.